The invention relates to an anti-buckling control system for steerable articulated vehicles, especially for articulated busses. Such articulated vehicles include a steerable forward wagon or unit and at least one hingedly connected following vehicular wagon or unit. The forward end of the following vehicular unit is pivotably connected about a cross axis with a cross girder or cross piece. The cross piece is pivotally borne for pivotal movement about a vertical axis at a rotary bearing support plate or table fixedly connected to the forward vehicular unit. The forward vehicular unit is further connected by means of two double acting piston-cylinder units articulatedly connected at the cross piece and the forward vehicular section in such a manner as to exhibit a V-shaped configuration when seen in the top view. The piston-cylinder units work in response to a computer operated control arrangement to forceably dampen the buckling angle between the forward and rearward vehicular units by means of exhausting and applying fluid pressure, preferably via a hydraulic medium, to the respective cylinder units.
An anti-buckling control system of the above mentioned general construction is proposed, including double acting piston-cylinder units, in the unpublished German patent application P 32 30 617.2. This construction is excellent with respect to the small space requirement needed. However, the arrangement of this application is in need of improvement in the arrangement of the piston-cylinder unit in so far as the same is articulated at the cross piece exactly inside of a vertical plane which intersects the pivot center of the cross piece. For example, if the piston-cylinder units are actuated to the buckling angle of the vehicular sections in a buckled condition of the vehicle, there is only a comparably small support moment because the axes of each piston-cylinder unit exhibits a very sharp (almost 180.degree.) angle with respect to the radius which leads from the buckling or pivot center of the cross piece to the cross piece sided ends of the respective piston-cylinder unit. This means that the piston-cylinder units support the cross piece in the buckled or pivoted condition of the vehicle with very short effective lever arms with respect to the pivot center of the cross piece.
In German published application (DE OS) No. 29 45 441, an arrangement is disclosed which deviates from the above-mentioned construction. According to this disclosure, two piston-cylinder units are disposed parallel to one another in a straight driving position of the vehicle and the piston-cylinder units are disposed at a lateral distance from the longitudinal axis of the vehicle between the front and rear vehicular sections. This design demands a considerable construction volume. Additionally, the piston-cylinder units are connected with the vehicular section by means of connecting links or guides such that with a buckled vehicle, as a rule only the piston-cylinder unit at the inside of the curve being traversed can transfer forces in the pushing direction; a simultaneous tranfer of tension forces through the piston- cylinder unit at the curve outside is, on the other hand, excluded.
A similar arrangement is described in German published application (DE-OS) No. 29 35 437. Here again, the two piston-cylinder units are disposed parallel to one another at opposite sides of the longitudinal axis of the vehicle middle with an extended straight position of the vehicle. The piston-cylinder units are connected to one vehicular section with only one of their ends while the other ends of the units abut the other vehicular section by means of bumbers. During the driving of the vehicle through a curve and the resultant buckling of the pivoted connection between the vehicular sections, only the piston-cylinder unit at the inside of the curve facilitates the application of compression forces; on the other hand the piston-cylinder unit at the outside of the curve can transfer neither tension nor compressive forces while it is even spaced from the bumper of the following wagon.
In addition, possibilites are described in the German published application (DE-OS) No. 30 04 409 for controlling the piston-cylinder units for damping the buckling angle changes at articulated vehicles. However, this publication contains no detailed statements about the manner of the arrangement of the piston-cylinder units between the two pivotally connected vehicular sections or wagons.
An object or problem of the invention is to improve an arrangement of the above-mentioned construction so that very high support moments between the cross piece and the wagon or vehicular unit connected therewith can be transferred by means of the piston-cylinder units, while maintaining a small construction space requirement.
These objects are achieved and problems solved according to the invention by providing that the ends of the piston-cylinder units connected to the cross piece are pivotally connected at the cross piece at the following wagon side of the vertical buckling pivot axis, when the vehicle is in a straight driving condition. In preferred embodiments, the arm connecting the following wagon with the cross piece are pivotally connected at a cross axis of the cross piece extending through the vertical buckling pivot axis.
With the arrangement of the invention, the respective piston-cylinder units are connected with a relatively large lever arm with respect to the buckling pivot axis of the cross piece when the vehicle is in a buckled position with the forward and rearward vehicular units at an angle to one another. In the buckled position, the axis of the piston-cylinder unit at the curve inside side of the vehicle forms an approximately right angle with a radius extending from the buckling pivot axis to the end of said piston-cylinder unit attached at the cross piece. Consequently, correspondingly high rotational moments can be accommodated, which as a rule are experienced during strong damping of the buckling angle changes or during a blockage of the piston-cylinder units for limiting the buckling angle during the course of driving conditions with a buckled connection.
Preferably the arrangement is so constructed that the piston-cylinder unit at the curve inside side of the vehicle forms approximately a right angle with the radius from the cross piece buckling axis to the end of said piston-cylinder connected at the cross piece during maximum buckling angle permitted by the design. Such an arrangement creates an especially large supporting moment with especially large buckling angles during which the following wagon can especially easily break out of the curve inside or outside e.g. jackknife.
The piston-cylinder unit at the curve outside side of the vehicle extends approximately parallel to the longitudinal axis of the forward wagon during a driving condition of maximum design buckling angle, however without running over the dead center position. With this construction, the piston-cylinder units exhibit a relatively large piston stroke during buckling of the vehicle section, a feature which is very advantageous with respect to accurate control.
In practical embodiments, the piston-cylinder units are disposed in a plane which is parallel to the plane of the rotary plate forming the buckling pivot support and attached to the forward wagon. This arrangement precludes the transfer of forces with vertical components to the cross piece.
Furthermore, the piston-cylinder units are preferably arranged above the rotary plate buckling pivot support because on the one hand, there is relatively much space available above the rotary plate and, on the other hand, the piston-cylinder units are effectively sheltered during driving conditions.
According to an especially advantageous embodiment of the invention, the computer control system for controlling the piston-cylinder units includes a failure recognition feature and a mechanism for opening a normally closed bypass line for the blocking and connection lines of the piston-cylinder fluid medium circuit upon the occurrence of a failure. This arrangement assures safe further driving also upon failures in the control system for the articulation interlock.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.